The invention relates to fuel injection systems, and more particularly to spark ignition direct injection systems.
Spark ignition direct injection systems are known for directly injecting fuel into the combustion chamber of an internal combustion engine. Typically, the fuel injectors of prior art direct injection systems are installed into ports in the cylinder head and are then rigidly clamped to the cylinder head using various clamping devices. The fuel rail is then mounted on the injectors and secured to the engine.
Other prior art techniques dispose a compression spring or Belleville washers between the fuel rail and the injector and then secure the fuel rail to the engine so that the spring or washers bias the injector toward the cylinder head. Another prior art technique utilizes Belleville washers positioned between a threaded clamping nut and the injector. The clamping nut is screwed into the cylinder head and the Belleville washers urge the injector toward the combustion chamber and away from the clamping nut.
The present invention provides an improved spark ignition direct injection system that couples an improved spring assembly to a fuel injector. Unlike prior springs or washers used to bias injectors, the spring assembly of the invention utilizes the xe2x80x9csqueeze film effect,xe2x80x9d a form of viscous damping, to facilitate installation of the injector into the cylinder head, to achieve the necessary seating force to maintain proper seating in the cylinder head, and to substantially prevent unseating of the injector during operation of the injection system. The squeeze film effect permits insertion of the injector at assembly using only a modest force input, and yet substantially prevents the injector from being unseated by the much larger forces applied to the injector during engine knocking/backfiring. The resistive spring force generated by the spring assembly varies inversely with the speed and duration at which an input force is applied to the injector. In other words, the relatively slow and steady application of force to seat the injector in the cylinder head results in a relatively low resistive spring force generated in the spring assembly, while a sudden, impact-type force on the injector caused by an engine backfire will generate a much higher resistive spring force or clamping force in the spring assembly.
The spring assembly includes a housing sized to fit directly on the outer surface of a fuel injector, thereby minimizing the added space requirements of the overall injection system. A spring, preferably in the form of a plurality of alternatingly-oriented disc springs, and a high viscosity material (e.g., grease) are positioned in the housing between the outer surface of the injector and the inner surface of the housing to achieve the desired squeeze film effect.
In one aspect of the invention, a retainer is coupled to the housing to close the open end of the housing. In addition to closing the open end of the housing, the retainer also provides a seating surface against which one end of the spring is seated. The retainer is at least partially received in the housing and is movable within the housing to accommodate retraction and expansion of the spring.
In another aspect of the invention, the retainer is comprised of first and second retainer members. One of the retainer members includes a concave surface and the other retainer member includes a convex surface movably engaged with the concave surface. When the injector is coupled to the fuel rail, the mating concave and convex surfaces permit the injector to pivot or tilt with respect to the fuel rail. This arrangement substantially eliminates bending moments on the injector that could otherwise be created by lateral misalignment between the fuel rail and the injector.
The invention also provides a method of seating and maintaining a fuel injector in an injector port of a cylinder head when the fuel injector is sandwiched between the fuel rail and the cylinder head. The method includes coupling the spring assembly to the fuel injector between the cylinder head and the fuel rail, and resisting the unseating of the injector from the injector port via the squeeze film effect created by the cooperation of the spring, the housing, and the viscous material of the spring assembly. A large resistive spring force or clamping force is generated in the spring assembly when a sudden force is applied to the injector in the direction of the fuel rail. The large clamping force operates to resist rapid movement of the injector toward the fuel rail.